Conventionally, a solar-radiation shielding device lifts and lowers a single solar-radiation shielding member by means of a plurality of lifting-cord winding mechanisms. The lifting-cord winding mechanism winds, around a winding drum, a lifting-cord that lifts and lowers the solar-radiation shielding member, where the winding drum is fitted to a drive shaft so that the winding drum is rotatable integrally with a drive shaft disposed in a head rail along the axial direction of the head rail. With the drive shaft rotating in one direction, the lifting-cord is wound onto the winding drum, which lifts the solar-radiation shielding member. With the drive shaft rotating in the opposite direction, the lifting-cord is reeled out of the winding drum, which lowers the solar-radiation shielding member.
According to a lifting-cord winding mechanism disclosed in Japanese Patent Publication Gazette No. 05-248156, the mechanism functions such that a lifting-cord is inserted through an entrance hole of a case fixed to a head rail having a bottom opening, with the tip of the lifting-cord fixed to a driving shaft directly or via a ring, and a winding drum is formed so as to have a larger diameter on one side thereof where the entrance hole is located, thereby preventing the lifting-cord from unaligned winding and partially overlapped winding. Since this prior art example enables the lifting-cord, wound around the external circumferential surface of the winding drum, to be wound uniformly, the solar-radiation shielding member is not likely to be lowered unevenly even when a plurality of lifting-cord winding mechanisms are used. This example however has a problem in that, since the position where the tip of the lifting-cord is attached on the winding drum is distant from the entrance hole, much surplus length of the lifting-cord remains in the head rail when the solar-radiation shielding member is lowered to a lower limit, thereby increasing the cost.
According to a lifting-cord winding mechanism disclosed in Japanese Patent Publication Gazette No. 11-206552, the mechanism functions such that a lifting-cord is inserted through a slit on the bottom of a case fixed to a head rail, with the tip of the lifting-cord attached to a ring fitted around a winding drum so that the ring is rotatable integrally with the winding drum but is slidable axially along the winding drum, and the ring is pushed along by the lifting-cord wound around the winding drum, thereby causing the wound lifting-cord to be well aligned on the circumferential surface of the winding drum. Little surplus length of the lifting-cord remains in the head rail when the solar-radiation shielding member is lowered to a lower limit. This example however has a problem in that, the lifting-cord, wound around the external circumferential surface of the winding drum, is likely to cause unaligned winding and partially overlapped winding, and is unable to be wound uniformly, whereby the solar-radiation shielding member is likely to be lowered unevenly when a plurality of lifting-cord winding mechanisms are used, thereby deteriorating the functionality and designing of the lifting-cord winding device.
Furthermore, with both the prior art examples, the winding drum restricts the hanging position of the lifting-cord, whereby the lifting-cord is unable to hang at an arbitrary position.
The present invention is made to solve the problems described above. Thus, an object of the present invention is to provide a lifting-cord winding mechanism of a solar-radiation shielding device wherein a lifting-cord for lifting a solar-radiation shielding member is enabled to be uniformly wound around a winding drum, the surplus length of the lifting-cord is made minimum that remains in a head rail when the solar-radiation shielding member is lowered to a lower limit, and the lifting-cord is enable to hang at an arbitrary position.